Electronic (e-) cigarettes are the newest and arguably the most popular non-cigarette products available to smokers, yet surprisingly few studies provide details on patterns of consumer uptake, nor on the impact of e- cigarette use on smoking. The majority of existing studies, which primarily use cross-sectional designs based on self-selected groups of e-cigarette users, provide only cursory indicators of use (e.g., never vs. ever vs. current), with little attention to details of uptake patterns. The science base is in strog need of a richer understanding of e-cigarette initiation among novel users, inclusive of 1) multiple indicators of the uptake process, 2) broad assessment of contextual antecedents of e-cigarette use, and 3) empirically derived understanding of how such ecological contexts trigger use. Equally needed is a strong understanding of how e-cigarette use impacts concurrent and downstream smoking behavior. A recurrent theme in the literature is the need for randomized clinical trials, but aside from two studies outside the U.S., neither of which is yet published, no such trial exists. This gap in the scientific base is especially pertinent in the U.S., wherein the FDA has classified e-cigarettes as a tobacco product and has expressed explicit intent to understand e- cigarettes - how smokers use them and what impact such use may have on smoking behavior. We propose the first prospective, randomized trial of e-cigarette use in the U.S. As a pilot (N=60), this study will provide important information for generation of future research, including large-scale trials that are so critically needed. Our trial includes a brief (3 week) sampling period, in which smokers with no prior e-cigarette use will be given the opportunity to use e-cigarettes (vs. not) as they wish. This sampling experience is wholly consistent with industry tactics, providing free samples and then assessing adoption and substitution, yet our independence from e-cigarette manufacturers is a clear study strength. The sampling period will assess naturalistic patterns of uptake via ecological momentary assessment (EMA) procedures to capture the context and nature of use in the real world. Our trial then transitions to prospective follow-up for an additional three months, during which we wil assess downstream effects of e-cigarette use on smoking behavior. Biological verification of nicotine intake throughout both the sampling and follow-up periods will provide prospective, objective indicators of nicotine exposure, which again strengthens the design and advances the literature. Our aims - to gather estimates of uptake with reasonable precision and to assess effect sizes in advance of a larger trial - are consistent with our methodological scope. We have strong experience in all proposed methods, including both small and large clinical trials that examine attitudes toward, uptake of, and behavioral effects of non-cigarette tobacco products among smokers. Our multidisciplinary team, in conjunction with expert consultants, comprises an outstanding study group that is ideally suited to this innovative proposal, which is offered in direct response to the FDA's intent to further understand the nature and impact of e-cigarette use.